The present invention relates generally to cerebrospinal fluid (CSF) shunts, and more specifically, to valves that variably moderate the siphoning effect of a hydrocephalus fluid shunt when the patient changes between recumbent and upright positions.
Hydrocephalus is a condition in which cerebrospinal fluid (CSF) accumulates in the ventricles of the brain. This accumulation of fluid increases the pressure within the ventricles and without medical intervention can cause brain damage and/or death to the patient. A common treatment for hydrocephalus is to use a fluid shunt system to drain excess CSF from the cerebral ventricles to a second body cavity, typically the peritoneal cavity. Shunt systems typically include a hollow catheter tube to remove CSF from the cerebral ventricles, a valve to regulate the CSF flow, and a discharge tube to conduct the CSF into the second body cavity. Such shunt systems are typically implanted entirely beneath the patient""s skin and remain in place for several weeks or more.
CSF shunt systems are generally effective when the patient is in a recumbent position. However, when the patient stands upright, the shunt system can act as a siphon resulting in over-drainage of CSF from the cerebral ventricles. The pathological consequences of over-drainage of CSF can include engorgement of the veins, cerebral edema, xe2x80x9cslit ventriclesxe2x80x9d and microcephaly.
To inhibit over-draining due to siphoning, some known CSF shunts have incorporated anti-siphoning devices (ASD) as part of their valve mechanisms. These ASD devices attempt to moderate the flow of the CSF when the patient""s attitude changes. The two most common types of mechanisms used in conventional anti-siphoning valves are weighted ball check valves and diaphragm valves.
Weighted ball check valves use one or more spherical balls that are more dense than CSF and are disposed within a cavity in the valve housing. The check valve is generally implanted such that the housing is oriented horizontally when the patient is in a recumbent position. The check valve includes a valve seat at the CSF inlet end (the distal end of the drainage catheter) for engaging the spherical ball. When the patient is recumbent, the spherical ball tends to move away from the valve seat, thereby permitting CSF to flow through the valve. As the patient changes orientation by sitting upright or standing, the valve is then oriented vertically with the valve seat at the bottom of the valve. The spherical ball, being denser than the CSF, sinks toward the valve seat and, when seated, stops the flow of the CSF.
Diaphragm-type anti-siphon valves include an elastic diaphragm to regulate CSF flow. The diaphragm is designed to bear against a seat with a force that is a function of the fluid pressure flowing from the cerebral ventricles, the pressure in the drainage tube, and a reference pressure (usually atmospheric pressure) on the opposite surface of the diaphragm. Under normal operation there is little resistance to the flow of the CSF. However, if the patient""s attitude is changed by sitting or standing up, the pressure in the discharge tube will fall as the column of fluid drains. This will increase the pressure differential across the diaphragm, thereby causing the diaphragm to seat more firmly against its seat, stopping the flow of CSF.
A major drawback to both of these approaches is that they are static in nature. If the symptoms persist after these devices are implanted into patients there is typically no alternative but to surgically replace the device.
There exists a need for better mechanisms to regulate CSF pressure, particularly in ambulatory patients. A variable anti-siphon valve that can be adjusted to meet the needs of an individual patient without surgery would be desirable.
Variable anti-siphon devices are disclosed for use in cerebrospinal fluid shunt systems. Such devices can include a housing with an internal chamber, an adjustable barrier separating the chamber into two cavities, and a diaphragm that seats itself against the adjustable barrier with a seating force that is proportional to the pressure differential across it. The adjustable barrier advantageously allows the level of anti-siphon protection to be modified. In one embodiment, the height of the adjustable barrier may be varied. In another embodiment, the barrier is moved longitudinally within the internal chamber to vary the volume of each chamber.
The present invention farther discloses an apparatus that allows the barrier to be adjusted externally to the patient, i.e., without the need for a surgical incision to access the valve. The barrier may be adjusted by the application of an external magnetic field that is magnetically coupled to a mechanism disposed within the housing. In another embodiment the external adjustment is accomplished by a miniature electric motor disposed within the housing and energized by signals generated external to the body.
In a further embodiment, an anti-siphon device valve includes two parallel paths for fluid drainage. One of the paths includes adjustable anti-siphon protection to prevent fluid flow during and after the attitude of the patient changes. The second path has a high fluid flow resistance but no anti-siphon protection. The second path will allow the flow of fluid to relieve excessive pressure to avoid the danger of having an increase in intra-cranial pressure remaining untreated when the patient is standing.